Sara

Sara is first shown when Zed goes to Calm Hospital after taking Noa to be treated. He shows her a certain feathered pendulum that Noa had given him. She stares at the pendulum in a rather strange display of surprise. After Zed is later attacked by a teacher of Calm, who was actually a member of Task, Sara personally battles it out with him. This reveals that Sara herself is a shard caster and possesses a sense of duty to protect her son, or at least to get rid of this Task member. Most of this battle is not really shown because she never releases any spirit, but instead continuously threw fire shards. Though, Sara is later shown holding the body of this Task member, in which it can be assumed he is dead. After this, she appeared several times, showing up in strange places, watching as events unfolded.
She's part the Seekers. The Seekers are after the key spirits so they can never be used by bad people. Sara actually wants only one thing, Amil Gaoul. She'll do everything to get him, even if it means killing her own son.